Decorative coating film

ABSTRACT

The present disclosure provides a decorative coating film, which ensures and/or maintains millimeter wave transmission properties even though the decorative coating film is continuously used. The present disclosure relates to a decorative coating film formed on the surface of a resin substrate positioned in the pathway of a radar device, wherein the decorative coating film at least comprises: fine silver particles or fine silver alloy particles, nickel oxide, and a binding resin having light transmission properties, which binds the fine silver particles or the fine silver alloy particles dispersed in the decorative coating film with one another, wherein the shape of the nickel oxide is a wire shape.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims priority from Japanese patent applicationJP 2017-246049 filed on Dec. 22, 2017, the content of which is herebyincorporated by reference into this application.

BACKGROUND Technical Field

The present disclosure relates to a decorative coating film formed onthe surface of a resin substrate, in which fine particles of metal oralloy are bound to one another by a resin having light transmissionproperties.

Background Art

Conventionally, a vehicle such as an automobile is equipped with a radardevice such as a millimeter wave radar in the central position of thefront part thereof, in order to measure the distance from a forwardobstacle or a forward vehicle. In such a radar device, an electricalwave irradiated from the radar device, such as a millimeter wave, isemitted forward through a front grill or an emblem of the vehiclemanufacturer. The emitted electrical wave is reflected at an object suchas a forward vehicle or a forward obstacle, and this reflected wave isreturned to the radar device through the front grill or the like.

Accordingly, for a portion disposed in the beam pathway of the radardevice, such as a front grill or an emblem, a material or a paint, whichis capable of reducing electrical wave transmission loss and impartingdesired good appearance to the vehicle, is frequently used, and adecorative coating film is generally formed on the surface of a resinsubstrate.

On the other hand, since a silver coating film has high visible lighttransmittance and is excellent in terms of infrared shielding property,the silver coating film has been conventionally used for various typesof intended uses. Moreover, since such a silver coating film is alsoexcellent in terms of electrical wave shielding property, for example,the silver coating film is able to protect electronic devices causingmalfunction due to electrical wave from external electrical wave, or tosuppress the irradiation of electrical wave generated from theelectronic devices. Thus, the silver coating film is also used as anelectrical wave shielding film.

For instance, JP 2015-080934 A proposes a decorative coating film, whichcomprises fine silver alloy particles dispersed in the decorativecoating film, and a binding resin having light transmission properties,which acts to bind the fine silver alloy particles to one another. Suchfine silver alloy particles comprised in the decorative coating filmconsist of an alloy consisting of silver and nickel, and the fine silveralloy particles have nickel in an amount range of 1% by mass to 30% bymass with respect to the mass of sliver.

SUMMARY

However, it has been found that, in the case of the conventionaldecorative coating film, the electrical wave (millimeter wave)transmission properties of the decorative coating film are significantlydecreased due to the continued use.

The present disclosure has been made in view of such a point, and thepresent disclosure provides a decorative coating film capable ofensuring and/or maintaining millimeter wave transmission properties,even after the continued use thereof.

As a result of intensive studies, the present inventors have thoughtthat the millimeter wave transmission properties of the decorativecoating film are easily decreased on the surface of fine silverparticles, or fine particles consisting of a silver-nickel alloy or asilver-zinc alloy (fine silver alloy particles), due to the influence ofsurface plasmon resonance absorption. Specifically, the presentinventors have thought that, as shown in FIG. 11A, when fine silverparticles or fine silver alloy particles are irradiated with light, thefine silver particles or the fine silver alloy particles are vibrated bylight energy, and free electrons inside them move, so that the finesilver particles or the fine silver alloy particles are easilypolarized.

Thus, the present inventors have thought that, as shown in FIG. 11B,surface electromagnetic wave called “surface plasmon polariton” iseasily generated on the surface of fine silver particles or fine silveralloy particles, and that a specific wavelength of light is absorbed,and the energy of the fine silver particles or the fine silver alloyparticles is easily amplified (surface plasmon resonance absorption).The inventors have thought that a constitutional substance (bindingresin) present around the fine silver particles or fine silver alloyparticles thereby become brittle by the influence of such amplificationenergy, and the fine silver particles or the fine silver alloy particlesmove and/or aggregate, and are allowed to come into contact with oneanother, so that conduction occurs and transmission of a millimeter waveis inhibited.

Hence, the present inventors have focused on a substance capable ofreinforcing a constitutional substance (binding resin) present aroundfine silver particles or fine silver alloy particles in a decorativecoating film. The present inventors have assumed that, by allowing thedecorative coating film to comprise a substance capable of reinforcing aconstitutional substance that is present around the fine silverparticles or the fine silver alloy particles, even in the state of thefine silver particles or the fine silver alloy particles easilygenerating surface plasmon resonance absorption, the transition and/oraggregation of the fine silver particles or the fine silver alloyparticles themselves are suppressed and the millimeter wave transmissionproperties of the decorative coating film can be ensured and/ormaintained without causing contact between the fine silver particles orthe fine silver alloy particles.

The present disclosure has been made in view of such a point, and thepresent disclosure relates to a decorative coating film formed on thesurface of a resin substrate positioned in the pathway of a radardevice, wherein the decorative coating film at least comprises: finesilver particles or fine silver alloy particles, nickel oxide, a bindingresin having light transmission properties, which binds the fine silverparticles or the fine silver alloy particles dispersed in the decorativecoating film with one another, wherein the shape of the nickel oxide isa wire shape.

According to the present disclosure, since the decorative coating filmhas a structure which at least comprises fine silver particles or finesilver alloy particles dispersed in the decorative coating film, and abinding resin having light transmission properties, which binds thedispersed fine silver particles or fine silver alloy particles with oneanother, the decorative coating film can be a coating film havingelectrical wave transmission properties and electrical insulation, andalso apparently having metallic luster.

Moreover, in the decorative coating film according to the presentdisclosure, nickel oxide having a wire shape is dispersed. In someembodiments, the aspect ratio of such a wire shape is 3 or more, and thewire diameter of the wire shape is 1 nm to 20 nm. Thus, when comparedwith a decorative coating film that does not comprise such nickel oxidehaving a wire shape, or a decorative coating film comprising nickeloxide having another shape, the present decorative coating filmcomprising nickel oxide having a wire shape is reinforced, and thetransition and/or aggregation of the fine silver particles or the finesilver alloy particles are suppressed, and the embrittlement of thebinding resin is suppressed, so that the millimeter wave transmissionproperties of the decorative coating film can be ensured and/ormaintained without causing contact between the fine silver particles orthe fine silver alloy particles when the present decorative coating filmis continuously used, even in the state of fine silver particles or finesilver alloy particles easily generating surface plasmon resonanceabsorption.

Herein, when the decorative coating film does not comprise theabove-described nickel oxide, or when the decorative coating filmcomprises nickel oxide having another shape instead of theabove-described nickel oxide, a constitutional substance that is presentaround the fine silver particles or the fine silver alloy particles maybecome brittle by receiving amplification energy caused by the influenceof surface plasmon resonance absorption as a result of long-term outdoorexposure, and thereby, the fine silver particles or the fine silveralloy particles may move and/or aggregate and thus, may be contacted oneanother to generate conduction, so that transmission of a millimeterwave may be inhibited.

In some embodiments, the amount of the nickel oxide having a wire shapeaccording to the present disclosure is 1.5% by mass to 35.0% by mass asnickel with respect to the mass of silver. The amount of the nickeloxide according to the present disclosure is 1.5% by mass or more asnickel with respect to the mass of silver, so that the effects ofcontinuously ensuring and/or maintaining the above-described millimeterwave transmission properties can be sufficiently exhibited, and theattenuation of a millimeter wave after a weathering test can bemaintained at a small level. On the other hand, the amount of the nickeloxide according to the present disclosure is 35.0% by mass or less asnickel with respect to the mass of silver, so that a reduction in thebrightness of the decorative coating film can be suppressed, and themetallic luster of the decorative coating film can be ensured withoutbeing impaired.

In some embodiments, the mean particle diameter (mean primary particlediameter) of the fine silver particles or the fine silver alloyparticles according to the present disclosure is 2 nm to 200 nm. Whenthe mean particle diameter of the fine silver particles or the finesilver alloy particles is within this range, light is easily absorbed bythe fine particles as a result of a phenomenon called “surface plasmonresonance absorption.” However, even in this embodiment, the decorativecoating film is reinforced because of the presence of the nickel oxidehaving a wire shape in the decorative coating film, and even in the caseof using the fine silver particles or the fine silver alloy particleshaving such a size, a reduction in the millimeter wave transmissionproperties of the decorative coating film can be suppressed.

When the mean particle diameter of the fine silver particles or the finesilver alloy particles is greater than 200 nm, irregular reflection oflight is easily generated by the fine silver particles or the finesilver alloy particles, and thereby, silver luster is easily decreased.On the other hand, when the mean particle diameter of the fine silverparticles or the fine silver alloy particles is less than 2 nm, lightmade incident to the decorative coating film is hardly reflected.

In some embodiments, the fine silver particles or the fine silver alloyparticles according to the present disclosure are fine silver particles.When the fine silver particles or the fine silver alloy particlesaccording to the present disclosure are fine silver particles, themetallic luster as outward appearance can be further enhanced.

According to the decorative coating film according to the presentdisclosure, millimeter wave transmission properties can be ensuredand/or maintained, even though the decorative coating film iscontinuously used.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view showing a decorative coatingfilm according to an embodiment of the present disclosure;

FIG. 2 is a schematic view showing a configuration of the decorativecoating film shown in FIG. 1;

FIG. 3 is a schematic perspective view showing the relationship among afront grill (resin substrate) located forward of a vehicle, an emblem onthe surface thereof, and a radar device disposed inside of the vehiclebehind the resin substrate;

FIG. 4 is a schematic cross-sectional view showing the relationshipamong a front grill (resin substrate) located forward of a vehicle, anemblem on the surface thereof, and a radar device disposed inside of thevehicle behind the resin substrate;

FIG. 5 includes photographs showing the results obtained by analyzingthe crystal structure of the nickel oxide having a wire shape in thedecorative coating film according to Example 1 by FFT;

FIG. 6 is a photograph showing the results of a STEM (scanningtransmission electron microscope) analysis performed on the fine silverparticles and nickel oxide in the decorative coating film according toExample 1;

FIG. 7 includes photographs showing distribution of silver, carbon,oxygen and nickel in the decorative coating film according to Example 1by an EDX mapping analysis;

FIG. 8 includes photographs showing distribution of silver, carbon,oxygen and nickel in the decorative coating film according toComparative Example 4 by an EDX mapping analysis;

FIG. 9 is a graph showing the relationship between the mass ratio ofnickel to silver (nickel/silver) according to Examples 1 to 3 andComparative Examples 1 to 4, and the initial L* value (before aweathering test) of each of the decorative coating films comprising suchnickel;

FIG. 10 is a graph showing the relationship between the mass ratio ofnickel to silver (nickel/silver) according to Examples 1 to 3 andComparative Examples 1, 2 and 4, and the millimeter waveattenuation-increasing percentage of each of the decorative coatingfilms comprising such nickel due to a weathering test;

FIG. 11A is a schematic view showing a state in which fine silverparticles or fine silver alloy particles are polarized by light; and

FIG. 11B is a schematic view showing surface plasmon resonanceabsorption.

DETAILED DESCRIPTION 1. Regarding Decorative Coating Film

FIG. 1 is a schematic cross-sectional view showing an embodiment of thedecorative coating film of the present disclosure. FIG. 2 is a schematicview showing a configuration of the decorative coating film shown inFIG. 1. FIG. 3 and FIG. 4 are, respectively, a schematic perspectiveview and a schematic cross-sectional view each showing the relationshipamong a front grill (resin substrate) located forward of a vehicle, anemblem on the surface thereof, and a radar device disposed inside of thevehicle behind the resin substrate.

A decorative coating film 1 shown in FIG. 1 constitutes an emblemattached to the surface of a resin substrate 20 that is a front grill F.As shown in FIG. 3, a radar device D equipped forward of an automotivebody A is disposed behind the front grill F. In the present embodiment,as shown in FIG. 4, a millimeter wave L1 irradiated from the radardevice D is emitted forward, through the front grill F and the emblem Elocated on the surface thereof. The emitted millimeter wave L1 isreflected at an object such as a forward vehicle or a forward obstacle,and this reflected wave (millimeter wave L2) is turned to the radardevice D through the emblem E and the front grill F. As such, thedecorative coating film 1 (emblem) is formed on the surface of the resinsubstrate 20 positioned in the pathway of the radar device D.

Since the decorative coating film 1 is applied to the surface of theresin substrate 20 (front grill F) positioned in the pathway of theradar device, the decorative coating film 1 is a coating film havingelectrical wave transmission properties (electrical insulationproperties), and also apparently having metallic luster.

Specifically, as shown in FIG. 1, a transparent resin coating film 2 maybe further laminated on the decorative coating film 1 in a viewingdirection (X direction). The decorative coating film 1 acts as abrightening layer and the resin coating film 2 acts as a protectivelayer of the decorative coating film 1. The resin coating film 2 mayconsist of a transparent polymeric resin, and may also be an adhesiveseal to be adhered to the decorative coating film 1. Moreover, the resincoating film 2 may be attached to the decorative coating film 1 via atransparent adhesive agent or the like.

As shown in FIG. 2, the decorative coating film 1 comprises fine silverparticles consisting of silver or fine silver alloy particles 1 a, andnickel oxide having a wire shape 1 d. The fine silver particles or finesilver alloy particles 1 a, and the nickel oxide having a wire shape 1 dare dispersed in the decorative coating film 1. The decorative coatingfilm 1 further comprises a binding resin 1 b having light transmissionproperties, which binds the fine silver particles or fine silver alloyparticles 1 a dispersed in the decorative coating film 1 with oneanother.

In some embodiments, the fine silver particles or fine silver alloyparticles 1 a and the nickel oxide having a wire shape 1 d are dispersedin the state of primary particles (namely, in a state in whichindividual fine silver particles or fine silver alloy particles 1 a andthe nickel oxide having a wire shape 1 d are separated from oneanother). In addition, around the fine silver particles or fine silveralloy particles 1 a, a layer of protective agent (dispersant) 1 c, whichhas been used as a raw material at the stage of producing the finesilver particles or fine silver alloy particles 1 a, may be furtherformed.

In the after-mentioned method for producing the fine silver particles orfine silver alloy particles 1 a, the mean particle diameter of the finesilver particles or fine silver alloy particles 1 a can be controlledby, for example, adjusting the heating temperature and/or the heatingtime applied upon the production of the fine silver particles or finesilver alloy particles 1 a, or selecting the type of the protectiveagent 1 c.

In the after-mentioned method for producing the nickel oxide having awire shape 1 d, the shape of the nickel oxide can be controlled to be awire shape by, for example, adjusting the pH of a reaction solution usedupon the production of the nickel oxide having a wire shape 1 d.

The fine silver particles consisting of silver or fine silver alloyparticles 1 a, which are comprised in the decorative coating film 1, arediscontinuously dispersed. The nickel oxide having a wire shape 1 d, thebinding resin 1 b, and the protective agent 1 c, which are presentaround the fine silver particles or fine silver alloy particles 1 a, aresubstances having electrical insulation. Accordingly, individual fineparticles are electrically insulated from one another, and in someembodiments, individual fine silver particles or fine silver alloyparticles 1 a are electrically insulated.

Therefore, when an electrical wave is passed through the decorativecoating film 1, the attenuation of the electrical wave (millimeter wave)is extremely small, and as a result, the decorative coating film 1 canbe a coating film apparently having metallic luster, and also havingfavorable millimeter wave transmission properties.

Besides, in the present description, the term “millimeter wave” means anelectrical wave having a frequency band of approximately 30 GHz to 300GHz, among various types of electrical waves. The present millimeterwave can be specified, for example, by having a frequency band ofapproximately 76 GHz. Moreover, in the present description, the term“decorative coating film” means a constitutional element constitutingthe aforementioned emblem of a vehicle manufacturer or ornaments, whichare specific to a vehicle, and the like. Specifically, with regard tothe decorative coating film, an emblem or the like is formed on thesurface of a front grill that is a resin substrate.

Moreover, with regard to a method of evaluating the millimeter wavetransmission properties of an emblem assembly, an object is establishedbetween a transmitting antenna and a receiving antenna, which are facedto each other, and the millimeter wave transmission amount is thenmeasured, and the attenuation degree is then evaluated by comparing themillimeter wave transmission amount with that in the case of notestablishing the object.

In the present embodiment, with regard to the nickel oxide having a wireshape 1 d, the aspect ratio (wire length/wire diameter) of the wireshape is 3 or more. In some embodiments, the aspect ratio of the wireshape is 50 or more. In some embodiments, the aspect ratio of the wireshape is 100 or more. In some embodiments, the wire diameter of the wireshape is 1 nm to 20 nm. In some embodiments, the wire diameter of thewire shape is 1 nm to 10 nm.

In the present embodiment, the aspect ratio of the wire shape can bemeasured, for example, using STEM (scanning transmission electronmicroscope). The nickel oxide having a wire shape includes nickel oxidehaving a thin wire shape. The nickel oxide having a thin wire shapecannot be confirmed if the magnification is decreased in STEM while thenickel oxide having a thin wire shape cannot be fit in the screen if themagnification is increased in STEM. Even in the case of such a nickeloxide having a thin wire shape, it is clear from STEM that the aspectratio of the wire shape is in the above-described range.

The wire diameter of the wire shape can be measured, for example, usingSTEM. For instance, the wire diameter of the wire shape can be obtainedby measuring the wire diameter of each of 10 or more nickel oxideshaving a wire shape, which have been randomly selected from the STEMimage, and then calculating the mean value thereof.

In the present embodiment, by allowing the decorative coating film 1 tocomprise the nickel oxide having a wire shape 1 d, when compared with adecorative coating film that does not comprise the nickel oxide having awire shape 1 d, or a decorative coating film comprising nickel oxidehaving another shape instead of the nickel oxide having a wire shape 1d, the decorative coating film 1 is reinforced, and the transitionand/or aggregation of the fine silver particles or fine silver alloyparticles 1 a are suppressed, and the embrittlement of the binding resin1 b is suppressed, so that the millimeter wave transmission propertiesof the decorative coating film 1 can be ensured and/or maintainedwithout causing contact between the fine silver particles or fine silveralloy particles 1 a when the decorative coating film is continuouslyused.

Moreover, in the present embodiment, in decorative coating film 1, theamount of the nickel oxide having a wire shape 1 d ranges from 1.5% bymass to 35.0% by mass as nickel with respect to the mass of silver. Insome embodiments, the amount of the nickel oxide having a wire shape 1 dranges from 1.5% by mass to 10% by mass as nickel with respect to themass of silver. By using the nickel oxide having a wire shape 1 d thatsatisfies the aforementioned range, the brightness (metallic luster) ofthe decorative coating film 1 can be ensured, and the millimeter wavetransmission properties of the decorative coating film 1 can be ensuredand/or maintained, even after the continued use thereof.

Herein, in the present embodiment, when the amount of the nickel oxidehaving a wire shape 1 d is less than 1.5% by mass as nickel with respectto the mass of silver, the brightness of the decorative coating film 1can be ensured, but the millimeter wave transmission properties of thedecorative coating film 1 are decreased due to the continued usethereof, as is apparent from the after-mentioned experiment conducted bythe present inventors.

On the other hand, as the ratio of nickel to silver increases, thebrightness of the decorative coating film tends to be decreased. Whenthe amount of the nickel oxide having a wire shape 1 d is more than35.0% by mass as nickel with respect to the mass of silver, thebrightness of the decorative coating film 1 is decreased, and themetallic luster of the decorative coating film 1 is impaired, as isapparent from the after-mentioned experiment conducted by the presentinventors.

When nickel oxide having another shape is used instead of the nickeloxide having a wire shape 1 d, the decorative coating film is noteffectively reinforced, and the millimeter wave transmission propertiesof the decorative coating film 1 are decreased due to the continued usethereof, as is apparent from the after-mentioned experiment conducted bythe present inventors.

Herein, the millimeter wave transmission properties of the decorativecoating film due to the continued use thereof, which are described inthe present description, can be evaluated by measuring the millimeterwave transmission properties of the decorative coating film before andafter performing a weathering test on the decorative coating film. Theweathering test indicates an accelerated weathering test, in whichoutdoor exposure is simulated, using a xenon weather testing machine inaccordance with JIS B 7764.

In the present embodiment, the mean particle diameter (mean primaryparticle diameter) of the fine silver particles or fine silver alloyparticles 1 a is 2 to 200 nm. When the mean particle diameter of thefine silver particles or fine silver alloy particles 1 a is greater than200 nm, irregular reflection of light is easily generated by the finesilver particles or fine silver alloy particles 1 a, and this causes aneasy reduction in the metallic luster of the decorative coating film 1.On the other hand, when the mean particle diameter of the fine silverparticles or fine silver alloy particles 1 a is less than 2 nm, lightmade incident to the decorative coating film 1 is hardly reflected.

Herein, the term “fine particles” in the phrase “fine silver particlesor fine silver alloy particles” used in the present description means“nanoparticles.” Furthermore, the “nanoparticle” means a particle havinga mean particle diameter from several nano-orders to several hundreds ofnano-orders in the present description. An example of a method ofmeasuring the particle diameter of a nanoparticle is a method comprisingextracting fine silver particles or fine silver alloy particle in apredetermined range of an FE-SEM image or a TEM image from the image,and then obtaining a mean value of the diameters (diameter approximatedas a circle) of these fine particles, which is then defined as a meanparticle diameter thereof.

In general, since the mean particle diameter of the fine silverparticles or fine silver alloy particles 1 a is a nano-order, the energyof the fine silver particles or fine silver alloy particles 1 a iseasily amplified by a phenomenon called surface plasmon resonanceabsorption. As a result, a constitutional substance that is presentaround the fine silver particles or fine silver alloy particles 1 areceives such amplification energy, and thereby, the millimeter wavetransmission properties of the decorative coating film 1 are easilydecreased.

However, in the present embodiment, even if the mean particle diameterof the fine silver particles or fine silver alloy particles 1 a is inthis range, the decorative coating film 1 is reinforced by comprisingthe nickel oxide having a wire shape 1 d, and thus, even if thedecorative coating film 1 is continuously used, the transition and/oraggregation of the fine silver particles or fine silver alloy particles1 a are suppressed, and the embrittlement of the binding resin 1 b issuppressed, so that the millimeter wave transmission properties of thedecorative coating film can be ensured and/or maintained without causingcontact between the fine silver particles or fine silver alloy particles1 a.

Furthermore, in some embodiments, the crystallite diameter of the finesilver particles or fine silver alloy particles 1 a is in the range of 2nm to 98 nm. Herein, when the crystallite diameter is less than 2 nm,light made incident to the decorative coating film 1 is hardlyreflected. On the other hand, when the crystallite diameter is more than98 nm, an electrical wave (electromagnetic wave) is hardly transmittedthrough the decorative coating film 1.

In some embodiments of the present disclosure, the fine silver particlesor fine silver alloy particles 1 a are fine silver particles. When thefine silver particles or fine silver alloy particles 1 a are fine silverparticles, the metallic luster as outward appearance can be furtherenhanced.

The binding resin 1 b is a polymeric resin having light transmissionproperties, and has electrical insulation. Examples of such a bindingresin include an acrylic resin, a polycarbonate resin, a polyethyleneterephthalate resin, an epoxy resin, and a polystyrene resin.

In some embodiments, as mentioned above, the binding resin 1 b is aresin having an affinity with the protective agent 1 c. For example,when an acrylic resin having a carbonyl group is used as a protectiveagent 1 c, the same type of acrylic resin is selected as a bindingresin.

Further, in some embodiments, the amount of the fine silver particles orfine silver alloy particles 1 a comprised in the decorative coating film1 as a whole is 83% by mass to 99% by mass. When the amount of the finesilver particles or fine silver alloy particles 1 a is less than 83% bymass with respect to the mass of the decorative coating film 1 as awhole, the metallic luster caused by the fine silver particles or finesilver alloy particles 1 a of the decorative coating film 1 may not besufficient. On the other hand, when the amount of the fine silverparticles or fine silver alloy particles 1 a is more than 99% by masswith respect to the mass of the decorative coating film 1 as a whole,the adhesiveness to the resin substrate 20 caused by the binding resin 1b of the decorative coating film 1 may not be sufficient.

2. Method of Forming Decorative Coating Film 1

First, a colloidal solution of fine silver particles or fine silveralloy particles and nickel oxide having a wire shape is prepared.

In this production method, a reduction method in a liquid phase isapplied. Specifically, a reducing solution having reducing ability hasbeen prepared, and a protective agent (dispersant) has been dissolved inthis reducing solution, as necessary. Subsequently, nickel in an ionicstate (specifically, a nickel solution) and silver in an ionic state(specifically, a silver solution) are added to the reducing solution.Thereafter, the pH of the reaction solution is adjusted to be pH 6 to12. In some embodiments, the pH of the reaction solution is adjusted tobe pH 6 to 9. By adjusting the pH of the solution within theabove-described range, the shape of nickel oxide can be controlled to awire shape. Thereafter, the reaction solution is heated generally at 50°C. to 90° C. for 1 hour to 10 hours, so that silver is precipitated inthe form of fine silver particles or fine silver alloy particles, andalso, nickel is precipitated in the form of nickel oxide having a wireshape.

Herein, in a case where a protective agent is added, the growing speedof fine silver particles is controlled, so that the mean particlediameter of the fine silver particles is easily controlled. In someembodiments, a polymeric resin having high adhesiveness to fine silverparticles and also having a good affinity with a binding resin addedlater is used as a protective agent.

By changing the contents of the added silver ions, and optionally,metallic ions constituting a silver alloy, and nickel ions, thecomposition ratio of silver to nickel oxide can be adjusted. Inaddition, the mean particle diameter of the fine silver particles or thefine silver alloy particles can be controlled by adjusting the heatingtemperature and the heating time. Moreover, as described above, the meanparticle diameter of the fine silver particles or the fine silver alloyparticles can also be controlled depending on the type of the protectiveagent.

Subsequently, unreacted matters are removed from the produced solutionby filtration or the like, and the solvent is then replaced with asuitable solvent to prepare a colloidal solution. Then, a binding resinis added to the colloidal solution to obtain a paint used as a rawmaterial for the decorative coating film. This paint is applied to theresin substrate 20, and is then heated, so that the decorative coatingfilm 1 can be formed on the surface of the resin substrate 20.

Alternatively, the colloidal solution containing fine silver particlesor fine silver alloy particles and nickel oxide having a wire shape mayalso be produced by preparing a solution containing fine silverparticles or fine silver alloy particles and a solution containingnickel oxide having a wire shape, separately, then mixing the twosolutions with each other, and then, optionally purifying the mixedsolution.

EXAMPLES

Hereinafter, the present disclosure will be described based on thefollowing examples.

Example 1

15.9 g of DISPERBYK 190 (manufactured by BYK Japan K.K.) used as aprotective agent was added to 597 g of N,N-dimethylaminoethanol used asa reducing agent, and thereafter, a solution prepared by dissolving 8.0g of nickel nitrate and 220 g of silver nitrate in nitric acid was mixedwith the obtained mixture. The thus obtained mixture was blended whilebeing heated at 60° C. for 120 minutes, so that fine silver particleswere precipitated. During this operation, by adjusting the amount ofnitric acid for use in dissolution to control the pH of the reactionsolution to pH 8, nickel oxide having a wire shape was also precipitatedat the same time. Besides, the fact that the substance having a wireshape was nickel oxide was confirmed by performing a crystal structureanalysis according to FFT, which is shown in FIG. 5.

The produced reaction solution was filtrated according to UF filtrationat room temperature (25° C. to 30° C.) for 3 hours. The washing solutionfor use in the filtration was successively changed from pure water toethanol, so as to obtain a colloidal solution comprising fine silverparticles having a mean particle diameter (mean primary particlediameter) of 30 nm, and nickel oxide having a wire shape in an amount of1.5% by mass as nickel with respect to the mass of silver (wherein theamount of nickel was an analytical value measured by ICP). Moreover,ethanol was replaced with 1-methoxy-2-propanol using an evaporator, soas to obtain a colloidal solution comprising 19% of a solid content(silver and nickel oxide).

It is to be noted that the solid content in the obtained colloidalsolution was measured as follows.

First, a small aliquot was sampled from the colloidal solution andheated at 140° C. for 2 hours until the solvent was volatilized, and theresidue in the colloidal solution was then measured. As a result, it wasfound that the residue accounted for 20% of the colloidal solution.Thereafter, an aliquot of the residue was heated to 500° C., using athermogravimetric (TG measurement) apparatus, to burn organiccomponents, so as to measure the solid content of the residue. As aresult, it was found that the solid content of the residue accounted for95% of the residue. As described above, the solid content in thecolloidal solution was calculated to be 0.2×0.95×100=19%.

Next, to 300 g of the colloidal solution, a 1-methoxy-2-propanolsolution comprising 8% by mass of a binding resin component (the amountof the binding resin: 57×0.08=4.56 g) with respect to the solid contentin the colloidal solution (the amount of the solid: 300×0.19=57 g) wasadded, so as to produce a paint. Herein, as a binding resin, a twoliquid mixed-type resin comprising an acrylic resin as a main skeletonand having a silane coupling bond was used.

Subsequently, the obtained paint was diluted with 1-methoxy-2-propanolor with any given thinner to obtain a mixture. The obtained mixture wasapplied to a transparent resin substrate, using a spray, and was thensubjected to a heat treatment at 80° C. for 30 minutes, so as to form adecorative coating film.

Examples 2 and 3

A decorative coating film was formed in the same manner as that ofExample 1. The difference from Example 1 was that the ratio of silvernitrate to nickel nitrate was changed in Examples 2 and 3, so that theamount of nickel oxide in the decorative coating film of Example 2 couldbe 2.0% by mass as nickel with respect to the mass of silver and theamount of nickel oxide in the decorative coating film of Example 3 couldbe 35.0% by mass as nickel with respect to the mass of silver.

Comparative Examples 1 to 3

A decorative coating film was formed in the same manner as that ofExample 1. Comparative Example 1 was carried out to show thesignificance of addition of nickel oxide. Comparative Example 2 wascarried out to determine the lower limit value of nickel to silver.Comparative Example 3 was carried out to determine the upper limit valueof nickel to silver.

Comparative Examples 1 to 3 were different from Example 1 in thefollowing points. In Comparative Example 1, nickel nitrate was notadded. In Comparative Examples 2 and 3, the ratio of silver nitrate tonickel nitrate was changed, so that the amount of nickel oxide in thedecorative coating film of Comparative Example 2 could be 1.0% by massas nickel with respect to the mass of silver and the amount of nickeloxide in the decorative coating film of Comparative Example 3 could be40.0% by mass as nickel with respect to the mass of silver.

Comparative Example 4

Using a paint synthesized by a method other than the above-describedpreparation method, a decorative coating film was formed. ComparativeExample 4 was carried out to compare the properties of a decorativecoating film comprising fine silver particles and nickel oxide having ashape other than a wire shape, with the properties of the decorativecoating films of Examples 1 to 3, comprising fine silver particles andnickel oxide having a wire shape.

Differing from Example 1, the decorative coating film of ComparativeExample 4 comprises, instead of the nickel oxide having a wire shape,nickel oxide not having such a wire shape, in which shapes with a sizeof approximately 50 nm, such as spherical, polyhedral and platy shapes,are present, in an amount of 1.5% by mass as nickel with respect to themass of silver in the decorative coating film.

[Microscopic Observation]

The aspect ratio of the wire shape (wire length/wire diameter) and thewire diameter of the obtained nickel oxide having a wire shape in thedecorative coating film according to Example 1 were examined using ascanning transmission electron microscope (STEM). The results are shownin FIG. 6. Moreover, according to energy-dispersive X-ray spectroscopy(EDX) using a scanning transmission electron microscope (STEM),distribution of silver, carbon, oxygen and nickel, as well as the aspectratio of the wire shape and the wire diameter of the nickel oxide havinga wire shape in the decorative coating film according to Example 1 wereexamined. The results are shown in FIG. 7. FIG. 7 includes photographsshowing distribution of silver, carbon, oxygen and nickel in thedecorative coating film according to Example 1. In FIG. 7, the upperleft photograph is a photograph taken using STEM; the upper centerphotograph shows distribution of silver in the decorative coating filmby EDX; the upper right photograph shows distribution of carbon in thedecorative coating film by EDX; the lower left photograph showsdistribution of nickel in the decorative coating film by EDX; the lowercenter photograph shows distribution of oxygen in the decorative coatingfilm by EDX; and in each photograph, a light color portion correspondsto each element. In addition, the lower right photograph shows theoverlapping of the distributions of silver and nickel in the decorativecoating film by EDX. As a control, FIG. 8 includes photographs showingdistribution of silver, carbon, oxygen and nickel in the decorativecoating film according to Comparative Example 4 by an EDX mappinganalysis. In FIG. 8, the upper left photograph is a photograph takenusing STEM; the upper center photograph shows distribution of silver inthe decorative coating film by EDX; the upper right photograph showsdistribution of carbon in the decorative coating film by EDX; the lowerleft photograph shows distribution of nickel in the decorative coatingfilm by EDX; the lower center photograph shows distribution of oxygen inthe decorative coating film by EDX; and in each photograph, a lightcolor portion corresponds to each element. In addition, the lower rightphotograph shows the overlapping of the distributions of silver andnickel in the decorative coating film by EDX.

[Weathering Test (Sunshine Test)]

A weathering test (sunshine test) was performed on the decorativecoating films according to Examples 1 to 3 and Comparative Examples 1, 2and 4, using a xenon weather testing machine in accordance with JIS B7764. Thereafter, the millimeter wave transmission properties of thedecorative coating films according to Examples 1 to 3 and ComparativeExamples 1, 2 and 4 were measured before and after the weathering test,and thereafter, the millimeter wave attenuation-increasing percentagewas calculated. Moreover, the initial lightness L* of each of thedecorative coating films according to Examples 1 to 3 and ComparativeExamples 1 to 4, which is specified by the color system (L*, a*, b*) ofCIE 1976 color system (JIS Z 8729), was measured using a colordifference meter (CR400, manufactured by Konica Minolta).

FIG. 9 is a graph showing the relationship between the mass ratio ofnickel to silver (nickel/silver) according to Examples 1 to 3 andComparative Examples 1 to 4, and the initial L* value (before aweathering test) of each of the decorative coating films comprising suchnickel. FIG. 10 is a graph showing the relationship between the massratio of nickel to silver (nickel/silver) according to Examples 1 to 3and Comparative Examples 1, 2 and 4, and the millimeter waveattenuation-increasing percentage according to a weathering test of eachof the decorative coating films comprising such nickel.

[Result 1: Regarding Fine Silver Particles and Nickel Oxide]

As shown in FIGS. 6 and 7, the nickel oxide of Example 1 had a wireshape. In the nickel oxide having a wire shape shown in FIGS. 6 and 7,the length of the wire shape was 100 nm to 250 nm, the wire diameter was5 nm, and the aspect ratio was 20 to 50. The nickel oxide having a wireshape included nickel oxide having a thin wire shape. The nickel oxidehaving a thin wire shape could not be confirmed if the magnification wasdecreased in STEM while the nickel oxide having a thin wire shape couldnot be fit in the screen if the magnification was increased in STEM.Even in the case of such nickel oxide having a thin wire shape, it wasclear that the aspect ratio of the wire shape was 3 or more. Moreover,as shown in FIG. 7, the fine silver particles and the nickel oxide wereuniformly dispersed in the decorative coating film. As shown in FIG. 8,in Comparative Example 4, nickel oxide with a size of approximately 50nm, which did not have a wire shape, was distributed.

[Result 2: Regarding Lower Limit Value of the Ratio of Nickel OxideHaving Wire Shape]

When the decorative coating films according to Examples 1 and 2 werecompared with the decorative coating films according to ComparativeExamples 1, 2 and 4, the initial L* values were at the same level, asshown in FIG. 9. In addition, the initial L* values of Example 1 andComparative Example 4 were the same values. However, as shown in FIG.10, although the millimeter wave attenuation-increasing percentagesaccording to the weathering test of the decorative coating film ofComparative Example 1, which did not comprise nickel oxide having a wireshape, and the decorative coating film of Comparative Example 2comprising nickel oxide having a wire shape in an amount of 1.0% by massas nickel with respect to the mass of silver, were increased, themillimeter wave attenuation-increasing percentages according to theweathering test of the decorative coating film of Example 1 comprisingnickel oxide having a wire shape in an amount of 1.5% by mass as nickelwith respect to the mass of silver, the decorative coating film ofExample 2 comprising nickel oxide having a wire shape in an amount of2.0% by mass as nickel with respect to the mass of silver, and thedecorative coating film of Example 3 comprising nickel oxide having awire shape in an amount of 35.0% by mass as nickel with respect to themass of silver, were not changed.

This is considered because the decorative coating films according toExamples 1 to 3 comprised a larger amount of nickel oxide having a wireshape than the decorative coating films of Comparative Examples 1 and 2,and thus, the decorative coating films of Examples 1 to 3 were furtherreinforced. Thereby, it is considered that transition and/or aggregationof fine silver particles or fine silver alloy particles were suppressed,and that the millimeter wave transmission properties of the decorativecoating films could be ensured and/or maintained without causing contactbetween the fine silver particles or the fine silver alloy particles,even in the state of fine silver particles or fine silver alloyparticles easily generating surface plasmon resonance absorption. Inview of the foregoing, it is considered that the millimeter wavetransmission properties of the decorative coating films can be ensuredand/or maintained if the content of the nickel oxide having a wire shapein the decorative coating film is 1.5% by mass or more as nickel withrespect to the mass of silver.

[Result 3: Regarding Upper Limit Value of Ratio of Nickel Oxide HavingWire Shape]

As shown in FIG. 9, as the content of nickel increases, the initial L*value of the decorative coating film tends to be decreased. The initialL* values of the decorative coating films according to Examples 1 to 3were higher than that of the decorative coating film according toComparative Example 3, and metallic luster was observed in thedecorative coating film of Example 3. In contrast, in the decorativecoating film according to Comparative Example 3, metallic luster wasimpaired. This is considered because metallic luster derived from finesilver particles of Comparative Example 3 was impaired since thedecorative coating film according to Comparative Example 3 comprised alarger amount of nickel oxide. From these results, it is found that thebrightness of the decorative coating film can be ensured, and themetallic luster of the decorative coating film can be maintained if thecontent of the nickel oxide in the decorative coating film is 35.0% bymass or less as nickel with respect to the mass of silver.

[Result 4: Regarding Shape of Nickel Oxide]

As shown in FIG. 10, the millimeter wave attenuation-increasingpercentage according to the weathering test of the decorative coatingfilm according to Comparative Example 4 was larger than that of thedecorative coating film of Example 1. When the decorative coating filmaccording to Example 1 was compared with the decorative coating filmaccording to Comparative Example 4, the two decorative coating filmswere identical to each other in that their content of nickel was thesame, but the two decorative coating films were different from eachother in that the decorative coating film according to Example 1comprised nickel oxide having a wire shape, whereas the decorativecoating film according to Comparative Example 1 comprised nickel oxidehaving a shape other than the wire shape. In the view of the foregoing,it is considered that the decorative coating film was more effectivelyreinforced by the nickel oxide having a wire shape, and that themillimeter wave transmission properties of the decorative coating filmcould be ensured and/or maintained. It is considered that when the shapeof nickel oxide was not a wire shape, the decorative coating film wasnot effectively reinforced, and thus that the millimeter wavetransmission properties of the decorative coating film could not beensured and/or maintained even if the content of nickel oxide in thedecorative coating film was 1.5% by mass as nickel with respect to themass of silver, after the decorative coating film had been continuouslyused.

As given above, the embodiments of the present disclosure are describedin detail using drawings. However, specific configurations are notlimited to these embodiments, and even if design modifications arecarried out in a range that is not deviated from the gist of the presentdisclosure, such modifications are included in the present disclosure.

All publications, patents and patent applications cited in the presentdescription are herein incorporated by reference as they are.

DESCRIPTION OF SYMBOLS

-   1 DECORATIVE COATING FILM-   1 a FINE SILVER PARTICLES OR FINE SILVER ALLOY PARTICLES-   1 b BINDING RESIN-   1 c PROTECTIVE AGENT (DISPERSANT)-   1 d NICKEL OXIDE HAVING WIRE SHAPE-   2 RESIN COATING FILM-   20 RESIN SUBSTRATE-   A AUTOMOTIVE BODY-   F FRONT GRILL (RESIN SUBSTRATE)-   E EMBLEM (DECORATIVE COATING FILM)-   D RADAR DEVICE-   L1 IRRADIATED MILLIMETER WAVE-   L2 REFLECTED MILLIMETER WAVE

What is claimed is:
 1. A decorative coating film formed on a surface ofa resin substrate positioned in a pathway of a radar device, wherein thedecorative coating film at least comprises: fine silver particles orfine silver alloy particles, nickel oxide, and a binding resin havinglight transmission properties, which binds the fine silver particles orthe fine silver alloy particles dispersed in the decorative coating filmwith one another, wherein a shape of the nickel oxide is a wire shape.2. The decorative coating film according to claim 1, wherein an aspectratio of the wire shape is 3 or greater, and a diameter of the wireshape is 1 nm to 20 nm.
 3. The decorative coating film according toclaim 1, wherein the fine silver particles or the fine silver alloyparticles are fine silver particles, and an amount of the nickel oxideis 1.5% by mass to 35.0% by mass as nickel with respect to a mass ofsilver.
 4. The decorative coating film according to claim 2, wherein thefine silver particles or the fine silver alloy particles are fine silverparticles, and an amount of the nickel oxide is 1.5% by mass to 35.0% bymass as nickel with respect to a mass of silver.
 5. The decorativecoating film according to claim 1, wherein the fine silver particles orthe fine silver alloy particles have a mean particle diameter of 2 to200 nm.
 6. The decorative coating film according to claim 2, wherein thefine silver particles or the fine silver alloy particles have a meanparticle diameter of 2 to 200 nm.
 7. The decorative coating filmaccording to claim 3, wherein the fine silver particles or the finesilver alloy particles have a mean particle diameter of 2 to 200 nm. 8.The decorative coating film according to claim 4, wherein the finesilver particles or the fine silver alloy particles have a mean particlediameter of 2 to 200 nm.